Image forming apparatus

TECHNICAL FIELD

0001The present invention relates to an image forming apparatus provided with a drive transmission device for transmitting a driving force to a unit detachably mountable to an apparatus main assembly.

BACKGROUND ART

0002In recent years, in an image forming apparatus such as a printer, a copying machine, or the like, of an electrophotographic type, downsizing and improvement in operativity have been desired.

0003From the viewpoint of the improvement in operativity of the image forming apparatus, a process cartridge system in which a photosensitive member, a charging means, a developing means, a cleaning means, and the like are integrally assembled into a cartridge and the cartridge is detachably mountable to an image forming apparatus main assembly has been employed. By this cartridge system, the operativity was further improved, so that it became possible to easily perform maintenance of the above-described process means such as the developing means by a user himself (herself).

0004Similarly, an intermediary transfer member and the like of the image forming apparatus main assembly is also constituted as a unit and the unit is detachably mountable to the image forming apparatus main assembly to improve the operativity and a maintenance property.

0005Further, as the drive transmission device for stably transmitting a driving force to these units detachably mountable to the image forming apparatus main assembly with reliability, coupling performed by a combination of a projected portion XX and a corresponding recessed portion YY as shown in <figref idref="DRAWINGS">FIG. 26</figref> has been used.

0006In Japanese Laid-Open Patent Application (Tokkai) 2005-157112, a constitution in which a coupling pair is interrelated with an openable cover or the like and by an opening operation of the cover, an apparatus main assembly-side coupling is retracted from a unit-side coupling to disengage the coupling pair thereby to permit mounting and demounting of the unit is disclosed.

DISCLOSURE OF THE INVENTION

0007However, in order to disengage and engage the couplings in interrelation with an opening and closing operation of the cover, in addition to an opening and closing mechanism portion of the cover, there is need to provide a mechanism for disengaging and engaging the couplings. By this mechanism, an opening and closing operativity of the cover has been deteriorated and a resultant constitution has been complicated to invite an increase in cost.

0008For example, in the case where a link mechanism is provided on the cover in order to engage and disengage the couplings, disengagement and engagement of the couplings are performed every opening and closing load of the disengagement and engagement of the couplings is borne by the cover. The load such as a resistance required for disengaging and engaging the couplings is apt to be added to an operating force for opening and closing the cover. Particularly, in a color image forming apparatus in which four process cartridges are arranged, the load for disengaging and engaging the couplings becomes large and for that reason, the operativity for opening and closing the cover has been deteriorated.

0009Further, the link mechanism is required to have high rigidity. In addition, there are needs to increase a size of the link mechanism itself and to increase the rigidity of the cover, thus leading to increases in size and cost of the apparatus.

0010In order to solve the above-described problems, according to an aspect of the present invention, there is provided an image forming apparatus comprising:

0011an apparatus main assembly;

0012a unit detachably mountable to the apparatus main assembly;

0013a first coupling, provided on the apparatus main assembly, for being rotated by power from a driving source; and

0014a second coupling, provided on the unit, for being rotated by engaging with the first coupling,

0015wherein either one of the first coupling and the second coupling has a recessed shape and the other coupling has a projected shape, at least one of an outer peripheral portion of the projected-shape coupling and an inner peripheral surface of the recessed-shape coupling having an inclined surface,

0016wherein at least one of the first coupling and the second coupling is retractable toward a direction parallel to a rotation shaft thereof, and

0017wherein the image forming apparatus has a structure such that a rotation shaft of the second coupling is more movable than a rotation shaft of the first coupling in a disengaging direction of the unit by a force exerted in the disengaging direction of the unit when the unit is pulled out from the apparatus main assembly in a direction perpendicular to the rotation shaft of the first cartridge and then by movement of the rotation shaft, at least one of the first cartridge and the second cartridge is retracted along the inclined surface in the direction parallel to the rotation shaft.

0018These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a sectional view showing a major part of an image forming apparatus according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view showing a mounting and demounting direction of a unit according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIG. 3</figref> is a plan view showing the mounting and demounting direction of the unit according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIG. 4</figref> is a perspective view showing a major part of a drive transmission device according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIGS. 5(<i>a</i>) to 5(<i>d</i>)</figref> are perspective and plan views showing couplings according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIGS. 6(<i>a</i>) to 6(<i>c</i>)</figref> are schematic views showing a state of a driving cartridge and a driven cartridge before start of disengagement of an intermediary transfer unit according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIGS. 7(<i>a</i>) to 7(<i>c</i>)</figref> are schematic views showing a state in which contact between a first engaging portion and a second engaging portion according to Embodiment 1 of the present invention is eliminated.

<figref idref="DRAWINGS">FIGS. 8(<i>a</i>) to 8(<i>c</i>)</figref> are schematic views showing a distance between a rotation shaft of the driving cartridge and a rotation shaft of the driven cartridge according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIG. 9</figref> is a schematic perspective view showing a primary transfer (member) spacing means according to Embodiment 1 of the present invention (phase G).

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic perspective view showing the primary transfer spacing means according to Embodiment 1 of the present invention (phase H).

<figref idref="DRAWINGS">FIGS. 11(<i>a</i>) to 11(<i>c</i>)</figref> are perspective views showing other couplings according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIGS. 12(<i>a</i>) and 12(<i>b</i>)</figref> are plan views showing other phases of the couplings according to Embodiment 1 of the present invention.

<figref idref="DRAWINGS">FIGS. 13(<i>a</i>) to 13(<i>c</i>)</figref> are perspective views showing couplings according to Embodiment 2 of the present invention.

<figref idref="DRAWINGS">FIGS. 14(<i>a</i>) to 14(<i>c</i>)</figref> are schematic views showing a state of a driving cartridge and a driven cartridge before start of disengagement of an intermediary transfer unit according to Embodiment 2 of the present invention.

<figref idref="DRAWINGS">FIGS. 15(<i>a</i>) to 15(<i>c</i>)</figref> are schematic views showing a state in which contact between a first engaging portion and a second engaging portion according to Embodiment 2 of the present invention is eliminated.

<figref idref="DRAWINGS">FIGS. 16(<i>a</i>) to 16(<i>c</i>)</figref> are schematic views showing a distance between a rotation shaft of the driving cartridge and a rotation shaft of the driven cartridge according to Embodiment 2 of the present invention.

<figref idref="DRAWINGS">FIGS. 17(<i>a</i>) to 17(<i>c</i>)</figref> are perspective views showing other couplings according to Embodiment 2 of the present invention.

<figref idref="DRAWINGS">FIGS. 18(<i>a</i>) to 18(<i>c</i>)</figref> are perspective showing couplings according to Embodiment 3 of the present invention.

<figref idref="DRAWINGS">FIGS. 19(<i>a</i>) to 19(<i>c</i>)</figref> are schematic views showing a state of a driving cartridge and a driven cartridge before start of disengagement of an intermediary transfer unit according to Embodiment 3 of the present invention.

<figref idref="DRAWINGS">FIGS. 20(<i>a</i>) to 20(<i>c</i>)</figref> are schematic views showing a state in which contact between a first engaging portion and a second engaging portion according to Embodiment 3 of the present invention is eliminated.

<figref idref="DRAWINGS">FIGS. 21(<i>a</i>) to 21(<i>c</i>)</figref> are schematic views showing a distance between a rotation shaft of the driving cartridge and a rotation shaft of the driven cartridge according to Embodiment 3 of the present invention.

<figref idref="DRAWINGS">FIGS. 22(<i>a</i>) to 22(<i>c</i>)</figref> are perspective views showing other couplings according to Embodiment 3 of the present invention.

<figref idref="DRAWINGS">FIG. 23</figref> includes sectional and perspective views showing the couplings according to Embodiment 4 of the present invention.

<figref idref="DRAWINGS">FIG. 24</figref> is a perspective view showing a mounting and demounting direction of a process cartridge.

<figref idref="DRAWINGS">FIG. 25</figref> is a plan view showing the mounting and demounting direction of the process cartridge.

<figref idref="DRAWINGS">FIG. 26</figref> is a perspective view showing a major part of a drive transmission device in the background art.

<figref idref="DRAWINGS">FIGS. 27A, 27B, 27C and 27D</figref> illustrate a slidable member and state changes with movement thereof, according to Embodiment 5 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

0046This embodiment will be described by using a four-drum type color image forming apparatus of an electrophotographic type as an apparatus main assembly and using an intermediary transfer unit as a detachably mountable unit. Further, in this embodiment, in order to transmit from the apparatus main assembly a driving force for moving a primary transfer roller in the intermediary transfer unit away from a corresponding photosensitive drum, a drive transmission device is used. The drive transmission device in this embodiment includes a first coupling and a second coupling rotating by being engaged with the first coupling.

0047Hereinbelow, an embodiment of the present invention will be described in the order of the image forming apparatus, the intermediary transfer unit, and the drive transmission device with reference to <figref idref="DRAWINGS">FIGS. 1 to 12</figref>.

0000[Image Forming Apparatus]

0048First, a constitution of an apparatus main assembly <b>100</b> will be described.

0049<figref idref="DRAWINGS">FIG. 1</figref> is a sectional view showing an embodiment of the image forming apparatus according to the present invention.

0000(1) Toner Image Forming Process

0050Formation of the toner image is performed by a photosensitive drum <b>1</b> as a photosensitive member, a charging roller <b>2</b> as a charging unit, an exposure unit <b>3</b>, a developing unit <b>4</b>, and the like. The apparatus main assembly <b>100</b> includes four photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>. Around each of the respective photosensitive drums <b>1</b>, along its rotational direction, the charging roller <b>2</b> (<b>2</b><i>a</i>, <b>2</b><i>b</i>, <b>2</b><i>c</i>, <b>2</b><i>d</i>) for electrically charging the surface of the photosensitive drum <b>1</b> uniformly and the exposure unit <b>3</b> for irradiating the photosensitive drum <b>1</b> surface with laser light on the basis of image information to form an electrostatic latent image on the photosensitive drum <b>1</b> are disposed in this order. Further, the developing unit <b>4</b> (<b>4</b><i>a</i>, <b>4</b><i>b</i>, <b>4</b><i>c</i>, <b>4</b><i>d</i>) for developing (visualizing) the electrostatic latent image as a toner image by depositing toner on the electrostatic latent image on the photosensitive drum <b>1</b>, and a transfer means <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c </i>or <b>12</b><i>d </i>for transferring the toner image from the photosensitive drum <b>1</b> onto an intermediary transfer belt <b>12</b><i>e </i>are disposed. Further, a cleaning means <b>8</b> (<b>8</b><i>a</i>, <b>8</b><i>b</i>, <b>8</b><i>c</i>, <b>8</b><i>d</i>) for removing transfer residual toner remaining on the photosensitive drum <b>1</b> surface after the transfer is disposed.

0051The photosensitive drum <b>1</b>, the charging roller <b>2</b>, the developing unit <b>4</b>, and the cleaning means <b>8</b> (<b>8</b><i>a</i>, <b>8</b><i>b</i>, <b>8</b><i>c</i>, <b>8</b><i>d</i>) are integrally assembled into a cartridge to prepare a process cartridge <b>7</b> (<b>7</b><i>a</i>, <b>7</b><i>b</i>, <b>7</b><i>c</i>, <b>7</b><i>d</i>). Each of the thus-prepared process cartridges is configured to be detachably mountable to the apparatus main assembly <b>100</b>. These four process cartridges <b>7</b><i>a</i>, <b>7</b><i>b</i>, <b>7</b><i>c </i>and <b>7</b><i>d </i>have the same structure but are different in that they form different color images by using a yellow (Y) toner, a magenta (M) toner, a cyan (C) toner, and a black (Bk) toner, respectively.

0052The process cartridges <b>7</b><i>a</i>, <b>7</b><i>b</i>, <b>7</b><i>c </i>and <b>7</b><i>d </i>are constituted by the developing units <b>4</b><i>a</i>, <b>4</b><i>b</i>, <b>4</b><i>c </i>and <b>4</b><i>d </i>are cleaning units <b>5</b><i>a</i>, <b>5</b><i>b</i>, <b>5</b><i>c </i>and <b>5</b><i>d</i>. Of these units, the former developing units <b>4</b><i>a</i>, <b>4</b><i>b</i>, <b>4</b><i>c </i>and <b>4</b><i>d </i>include developing rollers <b>24</b><i>a</i>, <b>24</b><i>b</i>, <b>24</b><i>c </i>and <b>24</b><i>d</i>, developer application rollers <b>25</b><i>a</i>, <b>25</b><i>b</i>, <b>25</b><i>c </i>and <b>25</b><i>d</i>, and toner containers. The latter cleaning units <b>5</b><i>a</i>, <b>5</b><i>b</i>, <b>5</b><i>c </i>and <b>5</b><i>d </i>includes the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>, the charging rollers <b>2</b><i>a</i>, <b>2</b><i>b</i>, <b>2</b><i>c </i>and <b>2</b><i>d</i>, the cleaning means <b>8</b><i>a</i>, <b>8</b><i>b</i>, <b>8</b><i>c </i>and <b>8</b><i>d</i>, and transfer residual toner containers.

0053The photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are constituted by applying an organic photoconductor (OPC) layer onto an outer peripheral surface of an aluminum cylinder and are rotatably supported by flanges at their both end portions. By transmitting a driving force from a driving motor (not shown) to one end portion of each of the portions <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>, each photosensitive drum is rotationally driven in a clockwise direction indicated by an arrow in <figref idref="DRAWINGS">FIG. 1</figref>.

0054The charging rollers <b>2</b><i>a</i>, <b>2</b><i>b</i>, <b>2</b><i>c </i>and <b>2</b><i>c </i>are an electroconductive roller formed in a roller shape. These charging rollers are brought into contact with the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are a charging voltage is applied to the charging rollers by a power source circuit (not shown), so that the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are electrically charged uniformly. The exposure unit <b>3</b> is disposed vertically below the process cartridges <b>7</b> (<b>7</b><i>a</i>, <b>7</b><i>b</i>, <b>7</b><i>c</i>, <b>7</b><i>d</i>) and exposes the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>to light on the basis of an image signal.

0055In the toner containers, the color toners of yellow (Y), magenta (M), cyan (C) and black (Bk) are accommodated, respectively.

0056The developing rollers <b>24</b><i>a</i>, <b>24</b><i>b</i>, <b>24</b><i>c </i>and <b>24</b><i>d </i>are disposed adjacent to the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>, respectively. These developing rollers are rotationally driven by a driving portion (not shown) and are supplied with a voltage, thus effecting development of the electrostatic latent images into toner images on the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d. </i>

0057By the constitution described above, the toner images of Y, M, C and Bk are formed on the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>. The toner images formed on the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are successively primary-transferred onto the surface of the intermediary transfer belt <b>12</b><i>e</i>. Thereafter, toners remaining on the surfaces of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are removed by the cleaning means <b>8</b><i>a</i>, <b>8</b><i>b</i>, <b>8</b><i>c </i>and <b>8</b><i>d </i>to be collected in the transfer residual toner container in the cleaning units <b>5</b><i>a</i>, <b>5</b><i>b</i>, <b>5</b><i>c </i>and <b>5</b><i>d. </i>

0000(2) Transfer onto Transfer Material and Fixing Process

0058Transfer of the toner images onto a transfer material S is performed at a secondary transfer portion <b>15</b> to which the transfer material S has been fed by a sheet feeding device <b>13</b>. The intermediary transfer unit <b>12</b> carries the toner images formed by the primary transfer process and conveys the toner images to the secondary transfer portion <b>15</b>. A fixing device <b>14</b> is located on a downstream side of the secondary transfer portion <b>15</b> and fixes the toner images, transferred on the transfer material S, on the transfer material S.

0059The sheet feeding device <b>13</b> is principally constituted by a sheet feeding cassette <b>11</b>, a sheet feeding roller <b>9</b>, a separating means <b>23</b>, and a registration roller pair <b>10</b> for nip-conveying the transfer material S. The fixing device <b>14</b> is constituted by a fixing film <b>14</b><i>a</i>, a pressing roller <b>14</b><i>b</i>, a heating element <b>14</b><i>c</i>, and a sheet discharging roller pair <b>20</b>.

0060The sheet feeding cassette <b>11</b> can be pulled out in a frontward direction of the apparatus main assembly <b>100</b> (a leftward direction of the apparatus main assembly <b>100</b> in <figref idref="DRAWINGS">FIG. 1</figref>). A user pulls out the sheet feeding cassette <b>11</b> from the apparatus main assembly <b>100</b> and then sets the transfer material S in the sheet feeding cassette <b>11</b> and inserts the sheet feeding cassette <b>11</b> into the apparatus main assembly <b>100</b>, so that supply of the transfer material S can be effected. The sheet feeding roller <b>9</b> press contacts the transfer material S accommodated in the sheet feeding cassette <b>11</b> and feeds the transfer material S by its rotation with predetermined timing, so that the transfer material S is separated and fed one by one by the separating means <b>23</b>. Thereafter, the transfer material S is conveyed to the secondary transfer portion <b>15</b> by the registration roller pair <b>10</b>.

0061At the secondary transfer portion <b>15</b>, a bias is applied to a secondary transfer means <b>16</b>, so that the toner images on the intermediary transfer belt <b>12</b><i>e </i>are transferred onto the transfer material S which has been conveyed to the secondary transfer portion <b>15</b>.

0062The fixing film <b>14</b><i>a </i>is an endless cylindrical belt and an outer peripheral surface thereof is disposed on a toner image surface side of the transfer material S. The heating element <b>14</b><i>c </i>is disposed inside the fixing film <b>14</b><i>a </i>and the pressing roller <b>14</b><i>b </i>opposes the heating element <b>14</b><i>c </i>through the fixing film <b>14</b><i>a </i>while press-contacting the fixing film <b>14</b><i>a</i>. The pressing roller <b>14</b><i>b </i>is rotationally driven by a driving means (not shown) to rotate the fixing film <b>14</b><i>a </i>correspondingly, so that the fixing film <b>14</b><i>a </i>is heated by the heating element <b>14</b><i>c</i>. The transfer material S conveyed from the secondary transfer portion <b>15</b> is nip-conveyed between the fixing film <b>14</b><i>a </i>and the pressing roller <b>14</b><i>b</i>, so that the toner images are heat-fixed on the transfer material S. The transfer material S on which the toner images are fixed is then nip-conveyed by the sheet discharging roller pair <b>20</b> and is discharged on a sheet discharge tray.

0000[Intermediary Transfer Unit]

0063In this embodiment, the intermediary transfer unit <b>12</b> is detachably mountable to the apparatus main assembly <b>100</b>. As shown in <figref idref="DRAWINGS">FIG. 2</figref>, the intermediary transfer unit <b>12</b> is configured to be detachably mountable to the apparatus main assembly <b>100</b> with respect to a direction A indicated by a double-pointed arrow.

0064The intermediary transfer unit <b>12</b> is principally constituted by the intermediary transfer belt (intermediary transfer member) <b>12</b><i>e</i>, a driving roller <b>12</b><i>f</i>, a follower roller <b>12</b><i>g</i>, the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c </i>and <b>12</b><i>d</i>, a cleaning means <b>22</b>, and a primary transfer (member) spacing means <b>30</b>. The intermediary transfer belt <b>12</b><i>e </i>is stretched around the driving roller <b>12</b><i>f </i>and the follower roller <b>12</b><i>g</i>. The follower roller <b>12</b><i>g </i>is urged in a direction E indicated by an arrow in <figref idref="DRAWINGS">FIG. 1</figref> by an urging means to apply a predetermined tension to the intermediary transfer belt <b>12</b><i>e. </i>

0065The driving roller <b>12</b><i>f </i>is rotationally driven by a motor (not shown) or the like, so that the intermediary transfer belt <b>12</b><i>e </i>is rotated at a predetermined speed in a direction F indicated by an arrow in <figref idref="DRAWINGS">FIG. 1</figref>.

0066Each of the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c </i>and <b>12</b><i>d </i>is disposed inside the intermediary transfer belt <b>12</b><i>e </i>so as to oppose an associated one of the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>and is urged toward the photosensitive drum <b>1</b> by an urging member <b>31</b>. By applying a voltage to the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c </i>and <b>12</b><i>d</i>, the toner images formed on the respective photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d </i>are primary-transferred onto the intermediary transfer belt <b>12</b><i>e</i>. On the intermediary transfer belt <b>12</b><i>e</i>, the four color toner images are superposedly transferred and then are conveyed to the secondary transfer portion <b>15</b>.

0067After the secondary transfer, the toner remaining on the intermediary transfer belt <b>12</b><i>e </i>is removed by the cleaning means <b>22</b> and is collected, by way of a transfer residual toner conveying path (not shown), in a toner collecting container (not shown) disposed in the apparatus main assembly <b>100</b>.

0068The intermediary transfer unit <b>12</b> has a spacing constitution for the primary transfer rollers, corresponding to Y, M and C, which oppose the associated ones of the photosensitive drums <b>1</b> while contacting the intermediary transfer belt <b>12</b><i>e </i>during color image formation. This spacing constitution is employed for suppressing sliding on the photosensitive drums <b>1</b> which are not used during monochromatic image formation and for prolonging the lifetime of the photosensitive drums <b>1</b>.

0069<figref idref="DRAWINGS">FIGS. 9 and 10</figref> show an example of the primary transfer spacing means <b>30</b> in this embodiment.

0070The primary transfer spacing means <b>30</b> is principally constituted by a cam shaft <b>32</b>, slidable members <b>33</b><i>a </i>and <b>33</b><i>b</i>, and cam members <b>34</b><i>a </i>and <b>34</b><i>b</i>. At both ends of the cam shaft <b>32</b>, the cam members <b>34</b><i>a </i>and <b>34</b><i>b </i>which have a symmetrical shape are disposed. The slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are provided at both ends of the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c</i>. The slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are moved leftward and rightward, so that positions of the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c </i>with respect to the respective photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b </i>and <b>1</b><i>c </i>can be changed.

0071During the color image formation, the cam members <b>34</b><i>a </i>and <b>34</b><i>b </i>are placed in a state of a phase G as shown in <figref idref="DRAWINGS">FIG. 9</figref> and the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are held in a state of a position J. As a result, the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c </i>and <b>12</b><i>d </i>contact the intermediary transfer belt <b>12</b><i>e </i>so as to oppose the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b</i>, <b>1</b><i>c </i>and <b>1</b><i>d</i>, respectively.

0072As shown in <figref idref="DRAWINGS">FIG. 10</figref>, the cam shaft <b>32</b> receives power by the drive transmission device (described later) to rotate the cam members <b>34</b><i>a </i>and <b>34</b><i>b </i>in a direction C indicated by an arrow, so that the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are moved in a direction D indicated by an arrow. During the monochromatic image formation, the cam members <b>34</b><i>a </i>and <b>34</b><i>b </i>are placed in a state of a phase H as shown in <figref idref="DRAWINGS">FIGS. 5(<i>a</i>) to 5(<i>d</i>)</figref>, so that the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are held in a state of a position K. The primary transfer rollers corresponding to Y, M and C are moved to and held at a retracted position, in which they are retracted from the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b </i>and <b>1</b><i>c</i>, by the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>with respect to a direction opposite to an urging direction, thus being spaced from the photosensitive drums <b>1</b><i>a</i>, <b>1</b><i>b </i>and <b>1</b><i>c</i>. When the cam members <b>34</b><i>a </i>and <b>34</b><i>b </i>are further rotated in the indicated direction C, they are returned to the phase G state and the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are also returned to the position J state.

0000[Driving Transmission Device]

0073A drive transmission device <b>40</b> in this embodiment includes a driving cartridge <b>31</b> as the first coupling and a driven cartridge <b>42</b> as the second coupling, which are described below The first coupling is provided on the apparatus main assembly <b>100</b> and is rotated by power from a driving source. The second coupling is provided on the intermediary transfer unit <b>12</b> and is rotated in engagement with the first coupling.

0074<figref idref="DRAWINGS">FIGS. 3 to 8</figref> show an example of the drive transmission device <b>40</b> in this embodiment. Hereinafter, the constitution of the drive transmission device <b>40</b> will be described.

0075To the apparatus main assembly <b>100</b>, the driving cartridge <b>41</b> as the first coupling, a driving motor <b>43</b>, a transmission gear <b>44</b><i>a</i>, and a guide member <b>46</b> are provided. The driving cartridge <b>41</b> as the first coupling is rotated by the power from the driving motor <b>43</b>. To the intermediary transfer unit <b>12</b>, the driven cartridge <b>42</b>, an urging member <b>45</b>, and a transmission gear train <b>44</b><i>b </i>are provided. As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the urging member <b>45</b> is a spring and urges the driven cartridge <b>42</b> in a direction B indicated by an arrow, i.e., toward the apparatus main assembly side. The driven cartridge <b>42</b> is disposed at a position, in which it opposes the driving cartridge <b>41</b>, in a state in which the intermediary transfer unit <b>12</b> is mounted in the apparatus main assembly <b>100</b>. The driven cartridge <b>42</b> as the second coupling is rotatable by being engaged with the driving cartridge <b>41</b> as the first coupling.

0076The guide member <b>46</b> is disposed in the apparatus main assembly <b>100</b> so that it contacts the driven cartridge <b>42</b> during mounting and demounting of the intermediary transfer unit <b>12</b>. Further, on an entrance side when the intermediary transfer unit <b>12</b> is mounted in the apparatus main assembly <b>100</b>, an inclined surface <b>46</b><i>a </i>for retracting the driven cartridge <b>42</b> in a direction M indicated by an arrow is provided.

0077As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the transmission gear <b>44</b><i>a </i>is disposed to connect the driving motor <b>43</b> and the driving cartridge <b>41</b>, and the transmission gear train <b>44</b><i>b </i>is disposed to connect the driven cartridge <b>42</b> and the cam shaft <b>32</b>.

0078As shown in <figref idref="DRAWINGS">FIGS. 5(<i>a</i>) and 5(<i>c</i>)</figref>, the driving cartridge <b>41</b> is provided on the apparatus main assembly <b>100</b>. Further, as shown in <figref idref="DRAWINGS">FIGS. 5(<i>a</i>) and 5(<i>b</i>)</figref>, the driven cartridge <b>42</b> has a projected shape engageable with the recessed shape. However, this embodiment is not limited to the above-described constitution but may employ a constitution in which one of the driving cartridge <b>41</b> and the driven cartridge has the recessed shape and the other coupling has the projected shape.

0079The driving cartridge <b>41</b> includes a T-shaped first engaging portion <b>41</b><i>b</i>. Further, the recessed-shape driving cartridge <b>41</b> has an inclined surface <b>41</b><i>e </i>at an inner peripheral surface portion thereof. The projected-shape driven cartridge <b>42</b> has second dc<b>1</b>

0080engaging portions <b>42</b><i>a </i>as projections. In a state in which the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are engaged with each other, the second engaging portions <b>42</b><i>a </i>of the driven cartridge <b>42</b> oppose an inner surface <b>41</b><i>a </i>of the driving cartridge <b>41</b>. Similarly, in the state in which the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are engaged with each other, the first engaging portion <b>41</b><i>b </i>of the driving cartridge <b>41</b> opposes an inner surface <b>42</b><i>b </i>of the driven cartridge <b>42</b>.

0081Further, the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are engaged with each other in a single phase, so that the driving force can be transmitted.

0082The inclined surface <b>41</b><i>e </i>of the driving cartridge <b>41</b> is provided at the inner peripheral portion of the driving cartridge <b>41</b> and contacts the second engaging portions <b>42</b><i>a </i>of the driven cartridge <b>42</b> in the state in which the intermediary transfer unit <b>12</b> is mounted in the apparatus main assembly <b>100</b>. The driven cartridge <b>42</b> is urged by the urging member <b>45</b> toward the driving cartridge <b>41</b> side in the direction B substantially perpendicular to the direction A which is a disengaging direction of the intermediary transfer unit <b>12</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. The direction B is parallel to rotation shafts (rotational axes) of both of the couplings.

0083The driving motor <b>43</b> is rotationally driven on the basis of a control signal, so that the driving cartridge <b>41</b> is rotated in a direction L indicated by an arrow. As shown in <figref idref="DRAWINGS">FIG. 5(<i>d</i>)</figref>, by the rotation of the driving cartridge <b>41</b>, contact surfaces <b>41</b><i>c </i>of the first engaging portion <b>41</b><i>b </i>are engaged with contact surfaces <b>42</b><i>c </i>of the second engaging portions <b>42</b><i>a</i>. That is, the contact surfaces <b>41</b><i>c </i>of the first engaging portion <b>41</b><i>b </i>of the driving cartridge <b>41</b> to which the driving force is to be transmitted from the driving motor <b>43</b> urge the contact surface <b>42</b><i>c </i>portions of the second engaging portions <b>42</b><i>a </i>of the driven cartridge <b>42</b>. As a result, a rotational force is transmitted from the driving cartridge <b>41</b> to the driven cartridge <b>42</b>, so that the driven cartridge <b>42</b> is rotated in the indicated direction L. At this time, the portions <b>41</b><i>c </i>and <b>42</b><i>c</i>, to which the rotational driving force is transmitted each other, have a shape such that the force with respect to the rotational direction is transferred. The contact surfaces <b>41</b><i>c </i>and <b>42</b><i>c </i>are engaged along an axial line substantially perpendicular to the rotational direction L, so that a force by which the driven cartridge <b>42</b> is urged in the rotation shaft direction opposite to the direction B as an urging direction is not generated during the rotation.

0084Next, the case where the intermediary transfer unit <b>12</b> is pulled out (disengaged from) the apparatus main assembly <b>100</b> will be described. When the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are engaged with each other, the second engaging portions <b>42</b><i>a </i>of the driven cartridge <b>42</b> contact the inclined surface <b>41</b><i>e </i>of the driving cartridge <b>41</b>. For this reason, when a force (pulling-out force) exerted in the disengaging direction of the intermediary transfer unit <b>12</b> is exerted, a force for moving the driven cartridge <b>42</b> in the indicated direction M opposite to the urging direction B is exerted on the driven cartridge <b>42</b> by the inclined surface <b>41</b><i>e</i>. Thus, the driven cartridge <b>42</b> is temporarily retracted from the driving cartridge <b>41</b> in the indicated direction M. As a result, the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are disengaged. Further, the driven cartridge <b>42</b> contacts the guide member <b>46</b> and is continuously retracted in the indicated direction M opposite to the urging direction B. Therefore, it is possible to pull out the intermediary transfer unit <b>12</b> from the apparatus main assembly <b>100</b>.

0085This will be described more specifically with reference to <figref idref="DRAWINGS">FIGS. 6(<i>a</i>) to 6(<i>c</i>)</figref> and <figref idref="DRAWINGS">FIGS. 7(<i>a</i>) to 7(<i>c</i>)</figref>. <figref idref="DRAWINGS">FIGS. 6(<i>a</i>) to 6(<i>c</i>)</figref> show a state of the driving cartridge and the driven cartridge before start of disengagement of the intermediary transfer unit, and <figref idref="DRAWINGS">FIGS. 7(<i>a</i>) to 7(<i>c</i>)</figref> show a state in which the first engaging portion <b>41</b><i>b </i>and the second engaging portions <b>42</b><i>a </i>are disengaged.

0086<figref idref="DRAWINGS">FIG. 6(<i>a</i>)</figref> and <figref idref="DRAWINGS">FIG. 7(<i>a</i>)</figref> are perspective views showing the state of the driving cartridge <b>41</b> and the driven cartridge <b>42</b>, and <figref idref="DRAWINGS">FIG. 6(<i>b</i>)</figref> and <figref idref="DRAWINGS">FIG. 7(<i>b</i>)</figref> are schematic views showing the state of the driving cartridge <b>41</b> and the driven cartridge as seen from the direction perpendicular to the rotation shaft. <figref idref="DRAWINGS">FIG. 6(<i>c</i>)</figref> and <figref idref="DRAWINGS">FIG. 7(<i>c</i>)</figref> are schematic views showing the state of the driving cartridge <b>41</b> and the driven cartridge <b>42</b> as seen from the direction parallel to the rotation shafts.

0087Before the intermediary transfer unit is disengaged, as shown in <figref idref="DRAWINGS">FIG. 6(<i>b</i>)</figref>, of the second engaging portions <b>42</b><i>a</i>, the second engaging portion (represented by <b>42</b><i>f </i>in <figref idref="DRAWINGS">FIG. 6(<i>c</i>)</figref>; hereinafter referred to as the second engaging portion <b>42</b><i>f</i>) of the driven cartridge located on the uppermost-stream side with respect to the intermediary transfer unit disengaging direction, and the contact surface <b>41</b><i>c </i>of the first engaging portion <b>41</b><i>b </i>of the driving cartridge are configured to create a sufficient gap therebetween with respect to the rotational direction. When the intermediary transfer unit is pulled out from the apparatus main assembly in the direction perpendicular to the rotation shaft of the rotation shaft of the driving cartridge <b>41</b>, by the force exerted in the disengaging direction of the intermediary transfer unit, the driven cartridge <b>42</b> is rotated so that the driven cartridge <b>42</b> approaches the contact surface <b>41</b><i>c</i>. At this time, the driven cartridge <b>42</b> is located at, as a center of the rotational movement, a position which is different from a position of the rotation shaft of the driving cartridge <b>41</b> and in which the driving cartridge <b>41</b> and the driven cartridge <b>42</b> contact each other. As shown in <figref idref="DRAWINGS">FIG. 6(<i>c</i>)</figref> and <figref idref="DRAWINGS">FIG. 7(<i>c</i>)</figref>, the second engaging portion located between the second engaging portion <b>42</b><i>f </i>and the first engaging portion <b>41</b><i>b </i>is represented by <b>42</b><i>h</i>. A position k in which the second engaging portion <b>42</b><i>h </i>and the contact surface <b>41</b><i>c </i>contact each other is referred to as a center k of the rotational movement in this embodiment.

0088When the driven cartridge <b>42</b> is started to be rotationally moved about the position k, the second engaging portion <b>42</b><i>f </i>approaches the contact surface <b>41</b><i>c </i>of the first engaging portion, so that the gap between the second engaging portion <b>42</b><i>f </i>and the contact surface <b>41</b><i>c </i>is decreased. When the driven cartridge <b>42</b> is rotationally moved, of the second engaging portions <b>42</b><i>a</i>, the second engaging portion (represented by <b>42</b><i>g </i>in <figref idref="DRAWINGS">FIG. 7(<i>c</i>)</figref>; hereinafter referred to as the second engaging portion <b>42</b><i>g</i>) of the driven cartridge located on the lowermost-stream side with respect to the intermediary transfer unit disengaging direction is moved the disengaging direction of the intermediary transfer unit along the inclined surface <b>41</b><i>e </i>of the driving cartridge. When the second engaging portion <b>42</b><i>g </i>is moved along the inclined surface <b>41</b><i>e</i>, the driven cartridge <b>42</b> is retracted in the direction M in <figref idref="DRAWINGS">FIGS. 7(<i>a</i>) and 7(<i>b</i>)</figref>. As a result, as shown in <figref idref="DRAWINGS">FIGS. 7(<i>a</i>) and 7(<i>b</i>)</figref>, the engagement between the first engaging portion and the second engaging portions is released. That is, the contact surfaces <b>42</b><i>c </i>of the second engaging portion are spaced from the contact surfaces <b>41</b><i>c </i>of the first engaging portion. As shown in <figref idref="DRAWINGS">FIGS. 7(<i>b</i>) and 7(<i>c</i>)</figref>, until the second engaging portions <b>42</b><i>a </i>and the first engaging portion <b>41</b><i>b </i>are disengaged, a distance at which the rotation shaft of the rotation shaft of the driven cartridge <b>42</b> is moved in the unit disengaging direction relative to the rotation shaft of the driving cartridge <b>41</b> is β.

0089Next, a structure such that the rotation shaft of the driven cartridge <b>42</b> is more movable than the rotation shaft of the driving cartridge <b>41</b> in the unit disengaging direction by the force exerted in the disengaging direction of the unit when the unit is pulled out from the apparatus main assembly in the direction perpendicular to the rotation shaft of the driving cartridge <b>41</b> will be described. As is understood from <figref idref="DRAWINGS">FIGS. 5(<i>a</i>) to 5(<i>d</i>)</figref>, the driven cartridge <b>42</b> is provided with a sufficient area in which the driving cartridge <b>41</b> is to be engaged. That is, in the case where the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are engaged with each other and are rotated, a gap is created therebetween.

0090As shown in <figref idref="DRAWINGS">FIGS. 8(<i>a</i>) to 8(<i>c</i>)</figref>, a maximum distance at which the rotation shaft of the driven cartridge <b>42</b> is movable in the unit disengaging direction with respect to the rotation shaft of the driving cartridge <b>41</b> is α. In this embodiment, α is configured to be larger than β. α is larger than β, so that when the driven cartridge <b>42</b> is rotationally moved about the position k, the retraction of the driven cartridge <b>42</b> into the direction M is completed before the second engaging portion <b>42</b><i>f </i>contact the first engaging portion <b>41</b><i>b. </i>

0091That is, in the coupling constitution in this embodiment, the engagement between the driven cartridge <b>42</b> and the driving cartridge <b>41</b> is released only by pulling out the intermediary transfer unit <b>12</b> from the apparatus main assembly <b>100</b>, so that the first engaging portion <b>41</b><i>b </i>and the second engaging portion <b>42</b><i>a </i>are disengaged.

0092Contrary to the above, in the case where the intermediary transfer unit <b>12</b> is mounted in the image forming apparatus main assembly <b>100</b>, the driven cartridge <b>42</b> contacts the guide member <b>46</b> of the apparatus main assembly <b>100</b>, so that the driven cartridge <b>42</b> is retracted in the indicated direction M. As a result, the driven cartridge <b>42</b> can be smoothly moved to an engaging position with the driving cartridge <b>41</b>. Further, in a state in which the rotation shaft (rotational axis) of the driven cartridge <b>42</b> and the rotation shaft (rotational axis) substantially coincide with each other, as described above, the couplings engage with each other when rotational phases of the couplings are in phase with each other, so that the mounting of the intermediary transfer unit <b>12</b> into the apparatus main assembly <b>100</b> is completed.

0093In this embodiment, by the engagement at a single phase, it is possible to transmit the driving force from the driving cartridge <b>41</b> to the driven cartridge <b>42</b>. As a result, on the basis of an amount of rotation of the driving motor <b>43</b>, it is possible to control the phase of the driven cartridge, i.e., the phase of the cam shaft <b>32</b> in this embodiment.

0094Further, this embodiment may only have a constitution in which one of the outer peripheral portion of the projected-shape coupling and the inner peripheral portion of the recessed-shape coupling has the inclined surface <b>41</b><i>e</i>. Further, as shown in <figref idref="DRAWINGS">FIGS. 11(<i>a</i>) to 11(<i>c</i>)</figref>, it is also possible to employ a constitution in which the second engaging portion <b>42</b><i>a </i>of the driven cartridge <b>42</b> also have the inclined surface, i.e., a constitution in which both of the outer peripheral portion of the projected-shape state and the inner peripheral portion of the recessed-shape state have the inclined surface. When both of the driving cartridge <b>41</b> and the driven cartridge <b>42</b> are provided with the inclined surface, the driven cartridge <b>42</b> can be further smoothly retracted in the indicated direction M opposite to the urging direction B. Incidentally, in the case of the phase shown in <figref idref="DRAWINGS">FIG. 12(<i>a</i>)</figref>, the driven cartridge <b>42</b> is rotationally moved about the position k shown in <figref idref="DRAWINGS">FIG. 12(<i>a</i>)</figref>, so that the driven cartridge <b>42</b> can be retracted along the inclined surface in the direction M. Further, in the case of the phase shown in <figref idref="DRAWINGS">FIG. 12(<i>b</i>)</figref>, the driven cartridge <b>42</b> can be retracted along the inclined surface in the direction M by the force exerted in the unit disengaging direction without being rotationally moved about the contact position between the second engaging portion <b>42</b><i>a </i>and the first engaging portion <b>41</b><i>b. </i>

Embodiment 2

0095In this embodiment, a drive transmission device in which a driving cartridge <b>51</b> and a driven cartridge <b>52</b> are engaged with each other at a plurality of phases will be described. All the constitutions other than the drive transmission device are similar to those in Embodiment 1.

0096In the case where there is no need to control the phase on an objective unit side by the driving motor provided on the main assembly side, a similar effect can be obtained also in the constitution of the couplings shown in <figref idref="DRAWINGS">FIGS. 13(<i>a</i>) to 13(<i>c</i>)</figref>. For example, a drive transmission device or the like for rotating unit-side rollers or the like in a predetermined direction corresponds to the constitution.

0097In <figref idref="DRAWINGS">FIGS. 13(<i>a</i>) to 13(<i>c</i>)</figref>, a reference numeral <b>51</b> represents a driving cartridge corresponding to the driving cartridge <b>4</b> in Embodiment 1 and a reference numeral <b>52</b> represents a driven cartridge corresponding to the driven cartridge <b>42</b> in Embodiment 1.

0098The couplings in this embodiment are similar to those in Embodiment 1 except that engaging portions of the driving cartridge <b>51</b> and the driven cartridge <b>52</b> are different in shape from the couplings in Embodiment 1.

0099As shown in <figref idref="DRAWINGS">FIGS. 14(<i>a</i>) to 14(<i>c</i>)</figref> and <figref idref="DRAWINGS">FIGS. 15(<i>a</i>) to 15(<i>c</i>)</figref>, similarly as in Embodiment 1, a distance at which the rotation shaft of the driven cartridge <b>52</b> is moved in the unit disengaging direction with respect to the rotation shaft of the driving cartridge <b>51</b> until a second engaging portion <b>52</b><i>a </i>and a first engaging portion <b>51</b><i>b </i>are disengaged is β.

0100Further, as shown in <figref idref="DRAWINGS">FIGS. 16(<i>a</i>) to 16(<i>c</i>)</figref>, similarly as in Embodiment 1, a maximum distance at which the rotation shaft of the driven cartridge <b>52</b> is movable in the unit disengaging direction with respect to the rotation shaft of the driving cartridge <b>51</b> is α. α is larger than β, so that when the driven cartridge <b>52</b> is rotationally moved about the position k, the retraction of the driven cartridge <b>52</b> into the direction M is completed before a second engaging portion <b>52</b><i>f </i>contacts the first engaging portion <b>51</b><i>b. </i>

0101Further, as shown in <figref idref="DRAWINGS">FIGS. 17(<i>a</i>) to 17(<i>c</i>)</figref>, the second engaging portion <b>52</b><i>a </i>of the driven cartridge <b>52</b> may also have an inclined surface <b>51</b><i>e</i>. When both of the driving cartridge <b>51</b> and the driven cartridge <b>52</b> are provided with the inclined surface, the driven cartridge <b>52</b> can be further smoothly retracted in the direction M opposite to the urging direction B.

Embodiment 3

0102In this embodiment, a drive transmission device in which a driving cartridge <b>61</b> and a driven cartridge <b>62</b> are engaged with each other at a plurality of phases will be described. All the constitutions other than the drive transmission device are similar to those in Embodiment 1.

0103Similarly as in Embodiment 2, the drive transmission device can be used in the case where there is no need to control the phase on an objective unit side by the driving motor provided on the main assembly side.

0104In <figref idref="DRAWINGS">FIGS. 18(<i>a</i>) to 18(<i>c</i>)</figref>, a reference numeral <b>61</b> represents a driving cartridge corresponding to the driving cartridge <b>4</b> in Embodiment 1 and a reference numeral <b>62</b> represents a driven cartridge corresponding to the driven cartridge <b>42</b> in Embodiment 1.

0105The couplings in this embodiment are similar to those in Embodiment 1 except that engaging portions of the driving cartridge <b>61</b> and the driven cartridge <b>62</b> are different in shape from the couplings in Embodiment 1.

0106As shown in <figref idref="DRAWINGS">FIGS. 19(<i>a</i>) to 19(<i>c</i>)</figref> and <figref idref="DRAWINGS">FIGS. 20(<i>a</i>) to 20(<i>c</i>)</figref>, similarly as in Embodiment 1, a distance at which the rotation shaft of the driven cartridge <b>62</b> is moved in the unit disengaging direction with respect to the rotation shaft of the driving cartridge <b>61</b> until a second engaging portion <b>62</b><i>a </i>and a first engaging portion <b>61</b><i>b </i>are disengaged is β.

0107Further, as shown in <figref idref="DRAWINGS">FIGS. 21(<i>a</i>) to 21(<i>c</i>)</figref>, similarly as in Embodiment 1, a maximum distance at which the rotation shaft of the driven cartridge <b>62</b> is movable in the unit disengaging direction with respect to the rotation shaft of the driving cartridge <b>61</b> is α. α is larger than β, so that the driven cartridge <b>62</b> can be smoothly retracted from the driving cartridge <b>61</b>.

0108Further, as shown in <figref idref="DRAWINGS">FIGS. 21(<i>a</i>) to 21(<i>c</i>)</figref>, the second engaging portion <b>62</b><i>a </i>of the driven cartridge <b>62</b> may also have an inclined surface <b>61</b><i>e</i>. When both of the driving cartridge <b>61</b> and the driven cartridge <b>62</b> are provided with the inclined surface, the driven cartridge <b>62</b> can be further smoothly retracted in the direction M opposite to the urging direction B.

Embodiment 4

0109In this embodiment, a function in the case where the driving cartridge <b>51</b> has an arcuate surface <b>42</b><i>i </i>and the arcuate surface abuts and contacts the driving cartridge <b>41</b> in the drive transmission device described in Embodiment 1 will be described with reference to <figref idref="DRAWINGS">FIGS. 23(<i>a</i>) to 23(<i>c</i>)</figref>. The reference numerals or symbols shown in <figref idref="DRAWINGS">FIGS. 23(<i>a</i>) to 23(<i>c</i>)</figref> are identical to those used in Embodiment 1.

0110The driven cartridge <b>42</b> is urged toward the driving cartridge <b>41</b> side by the urging member <b>45</b> and the arcuate surface <b>42</b><i>i </i>is configured to contact the inclined surface <b>41</b><i>e </i>of the driving cartridge <b>41</b> to determine a shaft direction position of the driven cartridge <b>42</b>.

0111Here, with respect to the apparatus main assembly <b>100</b>, also in the case where the position of the mounted intermediary transfer unit <b>12</b> is deviated within a range of variation, by employing the constitution in this embodiment, the rotational force can be transmitted even when eccentricity due to the positional deviation occurs to some extent.

Embodiment 5

0112As described in the foregoing embodiments, as shown in <figref idref="DRAWINGS">FIGS. 9 and 10</figref>, in the primary transfer spacing means <b>30</b>, when the operation mode shifts from the color image forming mode to the monochromatic image forming mode, the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>move from the position J to the position K. At this time, the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>move against the urging forces applied to the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c </i>by the urging member <b>31</b>. Therefore, the torque required to a driving motor <b>143</b> reaches the maximum when all the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c </i>are retracting simultaneously.

0113The structure of this embodiment is substantially the same as the structure of the foregoing embodiments with the exception that the slidable member is different.

0114<figref idref="DRAWINGS">FIGS. 27A, 27B, 27C and 27D</figref> illustrate another example of the primary transfer spacing means including a slidable member <b>30</b> according to this embodiment, in which the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c </i>are retracted stepwisely (not simultaneously). The slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>are provided with respective inclined surfaces <b>331</b><i>a</i>-<b>331</b><i>c </i>and <b>332</b><i>a</i>-<b>332</b><i>c </i>at the positions corresponding to the positions of the primary transfer roller <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c</i>. By the movement of the slidable members <b>33</b><i>a </i>and <b>33</b><i>b</i>, the primary transfer roller <b>12</b><i>a </i>rides on the inclined surfaces <b>331</b><i>a </i>and <b>332</b><i>a</i>, by which the transfer roller <b>12</b><i>a </i>retracts away from the photosensitive drum <b>1</b><i>a </i>against the urging force of the urging member <b>31</b>. Similarly, the transfer rollers <b>12</b><i>b </i>and <b>12</b><i>c </i>a retracted from the photosensitive drum <b>1</b><i>b </i>and <b>1</b><i>c </i>by the inclined surfaces <b>331</b><i>b </i>and <b>332</b><i>b </i>and the inclined surfaces <b>331</b><i>c </i>and <b>332</b><i>c</i>. More particularly, <figref idref="DRAWINGS">FIG. 27A</figref> shows a state in which the primary transfer roller <b>12</b><i>a </i>is starting to be raised (retracted from the photosensitive drum <b>1</b><i>a</i>) by the inclined surfaces <b>331</b><i>a </i><b>332</b><i>a</i>. As will be understood from this Figure, the gap between the inclined surface <b>331</b><i>a</i>, <b>332</b><i>a </i>and the surface of the shaft of the primary transfer roller <b>12</b><i>a </i>which are slidable on the inclined surface is smaller than the corresponding gap between the inclined surface <b>331</b><i>b</i>, <b>332</b><i>b </i>and the surface of the shaft of the primary transfer roller <b>12</b><i>b </i>which are slidable on the inclined surface, and the latter gap is smaller than the corresponding gap between the inclined surface <b>331</b><i>c</i>, <b>332</b><i>c </i>and the surface of the shaft of the primary transfer roller <b>12</b><i>c </i>which are slidable on the inclined surface.

0115Because of this structure, when the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>move in the direction indicated by the arrow D, the primary transfer roller <b>12</b><i>a </i>is first retracted from the photosensitive drum <b>1</b><i>a</i>, and then the primary transfer roller <b>12</b><i>b </i>is retracted from the photosensitive drum <b>1</b><i>b</i>, and subsequently the primary transfer roller <b>12</b><i>c </i>is retracted from the photosensitive drum <b>1</b><i>c. </i>

0116By offsetting the timings at which the primary transfer rollers <b>12</b><i>a</i>, <b>12</b><i>b </i>and <b>12</b><i>c </i>are retracted in the period of the slidable members <b>33</b><i>a </i>and <b>33</b><i>b </i>shifting from the position J to the position K in the direction indicated by the arrow D, the required maximum torque can be reduced.

0117Therefore, the primary transfer rollers are not simultaneously but sequentially retracted in the corresponding photosensitive drums. With this structure, the maximum required torque for sliding the slidable member <b>30</b> can be reduced, because it is not required to retract all of the primary transfer rollers simultaneously from the corresponding photosensitive drums, but it is enough if it can retract one of the primary transfer rollers away from the corresponding photosensitive drum.

0118These will be understood from <figref idref="DRAWINGS">FIGS. 27A, 27B, 27C and 27D</figref> which show the sequential changes of the positions of the primary transfer rollers with movement of the slidable member <b>30</b> in the direction indicated by the arrow D. That is, one primary transfer roller is retracted at a time. Finally, in the state of <figref idref="DRAWINGS">FIG. 27D</figref>, all of the primary transfer rollers are retracted from the corresponding photosensitive members.

0119According to this embodiment, the required specifications of the motor are lowered because they are enough if they can afford retraction of only one primary transfer roller, by which the cost of the drive transmission means for the movement of the slidable member <b>30</b> can be reduced.

Other Embodiments

0120In the above-described embodiments, the examples in which the couplings are used as the drive transmission device between the intermediary transfer unit <b>12</b> as the unit and the apparatus main assembly are described but the present invention is also applicable to other units and couplings. For example, the present invention is applicable to couplings between the developing unit (cartridge) and the apparatus main assembly and couplings between the process cartridge <b>7</b> in Embodiment 1 and the apparatus main assembly. As shown in <figref idref="DRAWINGS">FIGS. 24 and 25</figref>, a constitution in which the process cartridge <b>7</b> has the driven cartridge <b>42</b> may also be employed. Further, the shape represented by the reference numeral <b>41</b> is shown for the driving cartridge and the shape represented by the reference numeral <b>42</b> is shown for the driven cartridge but the present invention can be carried out even when a relationship between these shapes is reversed. Further, the functions of the driving cartridge <b>41</b> and the driven cartridge <b>42</b> with respect to the engagement are similarly performed even in a constitution in which either coupling is retracted, e.g., when the unit is mounted into the apparatus main assembly.

INDUSTRIAL APPLICABILITY

0121According to the present invention, engagement and disengagement of drive transmission couplings from the apparatus main assembly to the detachably mountable unit are performed automatically with mounting and demounting of the unit.

0122While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.